A pt reports having a "pins and needles" feeling in her left

Discussion in 'USMLE STEP 1' started by Guest, May 26, 2010.

  1. Guest

    Guest Guest

    A pt reports having a "pins and needles" feeling i

    A 37-year-old woman presents to her physician complaining of difficulty reading and fatigue. She reports having a "pins and needles" feeling in her left arm several months ago that resolved without treatment. On examination, visual field deficits and mild hyperreflexia are noted. MRI confirms the suspected diagnosis. Which of the following is the underlying mechanism of this patient's disease?


    A. Antibodies to acetylcholine receptors

    B. Axonal degeneration

    C. Demyelination of the peripheral nerves

    D. Loss of oligodendrocytes

    E. Loss of Schwann cells
  2. Guest

    Guest Guest

    Explanation:

    The answer is D. This woman presents with the classic signs and symptoms of multiple sclerosis (MS). A key to this disease is different neurological signs that are separated by space and time. (Another classic clue might have been oligoclonal bands on electrophoresis of the CSF.) MS is a demyelinating disease of the central nervous system, characterized by loss of oligodendroglial cells, which are the cells that are responsible for producing myelin in the central nervous system. Diagnosis can be confirmed by an MRI revealing sharply delineated regions of demyelination (plaques) throughout the central nervous system white matter (especially in periventricular areas).

    Antibodies to acetylcholine receptors (choice A) have been implicated in the etiology of myasthenia gravis, not multiple sclerosis.

    MS is generally characterized by axonal preservation, rather than degeneration (choice B).

    Demyelination of peripheral nerves (choice C) occurs in a number of diseases (e.g., Guillain-Barré), but not in MS. Guillain-Barré is characterized by ascending muscle weakness, areflexia, and paralysis.

    Oligodendrocytes are responsible for producing myelin in the central nervous system; Schwann cells (choice E) are responsible for myelination in the peripheral nervous system, and are not affected in multiple sclerosis.

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